1. Field of the Invention
The invention pertains to the field of fire hydrants. More particularly, the invention pertains to dry barrel fire hydrant main valves.
2. Description of Related Art
Fire hydrants were first invented in the early 1800's and followed the wide spread adoption of municipal water lines. By 1858, the cast iron dry-barrel hydrant was developed and became a ubiquitous curb-side fixture in urban areas throughout the US and much of the rest of the world, providing high pressure water at high volumes on nearly every city street.
The dry-barrel hydrant is particularly well suited to colder climates where low temperatures may freeze water in a hydrant and block the flow of water to the hydrant's outlets. Referring to the prior art FIG. 1, the dry-barrel hydrant is constructed in three major assemblies. An upper barrel 10, generally made of cast iron, is located above ground level and provided with outlet ports 40 for attachment of fire hoses. A barrel cap 50 at the top of the upper barrel 10 houses an operating stem nut 60 which may be turned to open or close the flow of water into the hydrant. This configuration defined the “fire plug” design which has since become almost universally recognizable.
The upper barrel 10 is connected to one end of a lower barrel 20 via a mating flange 70, 71, generally of a break-away design such that the upper barrel 10 can separate from the lower barrel 20 cleanly at the mating flange 70, 71, for example, if struck by an automobile. The lower barrel 20 provides a conduit through which water may flow from a location below the frost line, to the upper barrel 10 where it is needed for subsequent use in firefighting. The other end of the lower barrel 20 is similarly connected via a mating flange 80, 81 to an elbow 32 containing the hydrant's main valve assembly 31. The elbow 32 and main valve assembly 31 are shown in greater detail in prior art FIG. 2. The elbow 32 is also connected to a water main via an intervening gate valve (not shown) that can isolate the hydrant from the water main during installation, repair, or replacement of the hydrant. In this embodiment, a flange 34 is provided on one side of the elbow 32 for this purpose.
The operating stem nut 60 in the barrel cap 50 is threaded to one end of an operating stem 12 (including a breaking coupling 24, and operating stem extension 22) that traverses inside the upper barrel 10, the lower barrel 20, and is connected to the main valve assembly 31 inside the elbow 32 at its opposite end. Turning the operating stem nut 60, in turn, raises and lowers the operating stem 12 (and breaking coupling 24, and operating stem extension 22) and thus the main valve assembly 31 against, or away from, as shown for example in prior art FIG. 2, a main valve seat 33 located in the elbow 32 below a mating flange 80, 81 coupling the lower barrel 20 to the elbow 32. Thus, the elbow 32 has a “wet” side, below the main valve seal 36 inside the elbow 32, and a “dry” side above the main valve seal 36 and main valve seat 33.
The main advantage of this type of valve is that all main valve parts that are in contact with water, separating the “wet” and “dry” sides of the main valve seal 36, are located below the frost line, and therefore protected from freezing, and seizing, in cold temperatures, thus ensuring a reliable supply of water regardless of climate conditions.
As shown in prior art FIG. 2, and in more detail in prior art FIG. 3, drain holes 37 located in the elbow 32 and a valve seat insert 31 inset in the elbow 32, above the level of the main valve seal 36, allow the upper barrel 10 and lower barrel 20 to drain water to surrounding gravel beds or concrete basins once the hydrant main valve seal 36 has been closed against the main valve seat 33 after use. Hence, the term “dry barrel” hydrant is applied, as no water is present in the hydrant upper 10 and lower 20 barrels when the main valve seal 36 in the elbow 32 is closed.
As shown in prior art FIGS. 2-3, the main valve seal 36 is disposed between a main valve bottom plate 35 below the main valve seal 36, and a drain valve body 39 above the main valve seal 36. The operating stem extension 22 passes through the drain valve body 39, the main valve seal 36, and is threaded into the main valve bottom plate 35. Once assembled, drain valve pin 22A (prior art FIG. 3) inserted through the drain valve body 39 and the operating stem extension 22 prevents rotation of the operating stem extension 22 relative to the main valve bottom plate 35 during operation.
As shown in prior art FIGS. 2-3, the drain holes 37 are open to the inner volume of water above the main valve seal 36 when the main valve seal 36 is closed against the valve seat 33, and the upper barrel 10 and lower barrel 20 are allowed to drain (see arrows in prior art FIGS. 2-3). The drain valve body 39 is also provided with a drain valve facing 38, and a spring 38A which biases the drain valve facing 38 to move outwardly toward the valve seat 33. When the main valve seal 36 is opened by downward movement of the operating stem extension 22, the drain valve body 39 also moves downwardly such that the drain valve facing 38 is moved over the drain holes 37 in the elbow 32. The drain valve facing 38 is then held against the drain holes 37 through the spring 38A bias and high pressure water flowing past the main valve 36, effectively blocking the flow of water out of the drain holes 37 in the elbow 32.
This configuration has remained relatively unchanged since it was first developed. However, the main development considerations in the dry-barrel design have focused on anti-freezing, hydraulic efficiency, and ease of maintenance.
Hydraulic efficiency of the dry-barrel hydrant is primarily a function of the internal diameter of the upper barrel 10 and lower barrel 20 used, thus determining the maximum rate at which water can be delivered to the outlet ports 40 of the upper barrel 10. However, main valve seal 36 and valve seat 33 designs also affect hydraulic efficiency.
The elbow 32 is generally made of cast iron. The valve seat insert 31, as shown in prior art FIGS. 2-3, is typically made of bronze, or more recently stainless steel, and is permanently fitted to the elbow 32 where its flange 81 attaches to the lower barrel 20 via a mating flange 80. The main valve seat 33, also made of bronze or stainless steel, is then threaded into the valve seat insert 31 after the main valve seal 36 and operating stem assembly 12, 24, 22 have been lowered into the elbow 32, lower barrel 20, and upper barrel 10.
This valve design creates a stricture in the flow path at the point where the elbow 32 and lower barrel join 20, as the main valve seat 33 inner diameter is forced to be less than the inner diameter of the lower barrel 20 due to the thickness of the main valve seat 33 and valve seat insert 31. Typical lower 20 and upper 10 barrel internal diameters, shown in prior art FIG. 1 respectively as dl and du, are approximately 7 inches (17.8 cm), while the effective valve seat 37 inner diameter is only about 6 inches (15.2 cm).
Incorporation of removable main valve seats 33 has been required for installation of the drain valve body 39, main valve seal 36, and main valve bottom plate 35 assembly in the elbow 32, as the main valve seal 36 has a greater diameter than the main valve seat 33 inner diameter and must be located below the main valve seat 33 in the elbow 32.
Removable main valve seats 33 have also led to improved main valve seal 36 serviceability. Historically, a faulty main valve seal 36 could require excavation and replacement of the elbow 32 and the valve components contained therein. However, threaded main valve seats 33, and valve seat inserts 31, allow main valve seats 33 to be removed through the upper 10 and lower 20 barrel after removal of the barrel cap 50 by unthreading the main valve seat 33 from above.
Once unthreaded, the main valve seat 33, the main valve seal 36, drain valve body 39, and a main valve bottom plate 35 may be lifted out of the elbow 32 and barrels 10, 20 using the operating stem assembly 12, 24, 22 that connects the main valve bottom plate 35 and the stem operating nut 60 on the barrel cap 50. Once removed, the entire assembly may be further disassembled and individual components repaired or replaced.
While these designs have found widespread use, machining required to correctly mate the valve seat insert 31 to the elbow 32 increases manufacturing costs. Further, the presence of the valve seat insert 31 limits the internal diameter of the main valve seat 33 so that, for a given diameter lower barrel 20 and upper barrel 10, effective hydraulic efficiency is reduced. Also, time required to remove the main valve seat 33 for servicing increases maintenance costs of installed units.
As a result of these factors, space required for removal of the valve seat 33 through the upper 10 and lower 20 barrels requires a trade-off that results in either over dimensioning the internal diameters of the upper 10 and lower 20 barrels to accommodate a larger outer (and inner) diameter of the main valve seat 33 for removal, or, decreasing water flow by using a smaller diameter valve seat 33 to allow it to fit through smaller diameter upper 10 and lower 20 barrels. And in either case, the presence of the valve seat insert 31 always creates an additional flow restriction between the elbow 32 and the lower barrel 20.